1. Field of the Invention
This invention pertains generally to the field of machines for forming cartons, and particularly to such apparatus suitable for forming sealed pouches capable of carrying food materials.
2. Description of the Prior Art
Cartons or containers which are used to carry food products, particularly those in liquid form, must be securely sealed at those areas where the paperboard is joined in order to prevent leaks or contamination from material outside the package. Moreover, many common adhesive materials cannot be used to form the joints because such adhesives may not be compatible with food products, or may deteriorate in the presence of moisture, or may not provide the strong air-tight and liquid-tight seals that are required.
Food containers have been made by coating portions of the surface of the container blank with a material which can be activated by heat with sealing being obtained upon joining of the proper surfaces. Often, the entire surface of the carton will be coated with a heat sealable material such as polyethylene in order to make the interior of the carton substantially moisture proof. A container of this type which is well adapted for use in carrying food products is a paperboard pouch formed of a single blank folded in half, with the facing longitudinal side edges being heat sealed together in a "fin" seal. After insertion of the contents of the pouch, the top edges are then sealed together to completely enclose the contents. A pouch constructed in this manner has the advantage that seals need be formed only along the side edges and top of the pouch, and not along the bottom of the pouch where the stress imposed by the contents is apt to be greatest.
A number of machines have been developed that provide for the automatic formation and sealing of paperboard cartons or plastic material which is heat sealable. Examples of such machines capable of forming heat sealed cartons are shown in U.S. Pat. Nos. 3,448,588; 3,593,623; and 3,785,255. U.S. Pat. Nos. 3,633,333; 3,200,303; 3,980,515; and 4,019,946 are also known to show heat sealing of material to form enclosed containers. Such machines are generally not well adapted to the rapid production of heat sealed pouches formed from a single blank wherein only the longitudinal side edges and the top of the blank are being sealed.